import java.util.Scanner;

public class Test {
    //递归求 1 + 2 + 3 + ... + 10
    public static int sum(int n) {
        if(n == 1) {
            return 1;
        }
        return n+sum(n-1);
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int ret = sum(sc.nextInt());
        System.out.println(ret);
    }
}
